Two people have been charged with extortion after being arrested by detectives for allegedly trying to sell embarrassing information about singer Stevie Wonder.

Alpha Walker and his girlfriend Tamara Diaz have been in custody since their arrest on May 2. Both have pleaded not guilty and will appear in court in Los Angeles on May 16 for a hearing in which a judge will decide whether there is enough evidence for them to stand trial.

According to a felony complaint, Walker and Diaz attempted to obtain money from the Grammy-winning musician, who is identified by his birth name, Steveland Morris.

Walker, 38, was on probation at the time of his arrest after pleading no contest to grand theft in May 2011. A judge issued a suspended three-year prison sentence in that case and he is due in court for a probation violation hearing on May 31.

District attorney's spokeswoman Jane Robison said Walker contacted Wonder's representatives claiming to have embarrassing information about the musician.

Detectives organised a sting and the pair were arrested. Police did not release additional details about their investigation.

Walker identifies himself as Wonder's nephew and is being held without bail because of another case. Diaz's bail is set at 95,000 dollars (£59,300).

Diaz was placed on three years' probation after pleading no contest in February 2011 to possession of marijuana with the intent to sell, court records show.